The present invention relates to a capless writing tool which is so designed that when a writing body is stored, a front end writing portion of the writing body is held in a sealed state by a simple construction and which is suitably used particularly for a ballpoint pen using neutral ink.
A ballpoint pen using gel-like so-called neutral ink whose viscosity is lower than that of oily ink but higher than that of aqueous ink has become popular in recent years for the ink being free from dripping and blurring.
In the case of this neutral ink ballpoint pen, a cap is provided for sealing and protecting the front end writing portion. Such cap, as found in Japanese Utility Model Publication Sho 61-29592 and Japanese Utility Model Kokai Hei 1-139593, has a thick-walled or spherical sealing member of elastic material, such as rubber, so that the front end writing portion of the writing body inserted in the cap elastically abuts against or is slightly embedded in the sealing member, so as to fill the clearance between the writing ball of the front end writing portion and the embracing portion therearound, thereby preventing the drying, leakage and backflow of the ink.
However, the cap type writing tool must have its cap removed each time for writing, the donning and doffing operation being troublesome. Further, the removed cap is liable to be lost. In the case of a sealed cap, when the cap is put on the main body of the writing tool, the pressure in the cap increases, resulting in the air entering the writing body through a slight clearance between the writing ball and the embracing portion therearound; thus, it is also necessary to provide air circulation means in the cap itself.
Therefore, in the case of this neutral ink ballpoint pen also, it is desired to provide a capless writing tool which can dispense with the cap, which allows the front end writing portion to go in and out by a knocking operation, and which has a mechanism for preventing the drying, leakage and backflow of the ink.
In recent years, among capless writing tools adapted to project the front end writing portion at a touch as by a knock, there has appeared one provided with a mechanism for preventing the drying of the ink in the writing body.
As for a capless writing tool having this drying preventing mechanism, various suggestions have been made; for example, as found in Japanese Patent Kokai Hei 4-14880, Japanese Patent Kokai Hei 5-68360 and Japanese Utility Model Kokai Hei 2-112492, there is proposed one comprising an openable and closable seal cover installed on the front end of a seal sleeve disposed in the main body, the arrangement being such that the seal cover is opened and closed by the advancing and retracting action of the writing body through a string-like member installed to extend between the seal cover and the writing body.
The proposed mechanism is so designed that in the state in which the front end writing portion of the writing body is received in the seal sleeve, sealing is effected at two longitudinally spaced locations, one on the seal cover at the front end and the other on a seal portion, such as a circumferential ridge, closely contacting the outer periphery of the writing body disposed rearwardly of an air hole, thereby isolating the interior of the seal sleeve from the outside so as to maintain the sealed state. Thus, in a writing tool, such as a pad type aqueous ink ballpoint pen having an air hole in the vicinity of the front end writing portion, or a pad type aqueous or oily marker, the front end writing portion, together with the air hole, is maintained in the completely sealed state to prevent the drying of the ink.
In the case of the proposed drying preventing mechanism, however, the two seal portions complicate the sealing mechanism and, furthermore, since the clearance between the writing ball and the embracing portion therearound is not closed, it cannot be said to be in a sealed state, having almost no effect in preventing the drying, leakage and backflow of the ink.
That is, in the case of a neutral ink ballpoint pen, a rear end of the writing body is not in the completely sealed state and instead it is charged with gel-like fluid sealant which differs in specific gravity from ink and which is viscous and has fluidity, so as to prevent backflow of the ink and allow a decrease in the amount of ink, thereby enabling the pen to be used without any trouble even if the rear end of the writing body is open while dispensing with the air hole in the vicinity of the front end writing portion.
Therefore, up to now there has been no neutral ink ballpoint pen put into practical use which is capless and which can be made ready for writing by the knocking operation.